1. Field of the Invention
The invention relates to manhole cover supports and in particular to a separate ring placed within an existing manhole to raise the height of the manhole cover to compensate for added roadway pavement. More particularly, the invention relates to a manhole cover support ring which is mounted within an existing manhole frame opening and is expanded outwardly into clamping engagement with the manhole cover frame by a pivotally mounted tubular-bolt mechanism on the ring.
2. Description of the Prior Art
Most underground facilities, such as sanitary and storm sewers, utility conduits and the like, have manhole openings to provide access thereto. These manholes usually are located in the street or roadway and consist of an inverted bell-shaped metal frame mounted on top of a brick or concrete base structure. This metal frame has an internal ledge for supporting the manhole cover so that the top of the cover is level with the top of the frame and surrounding roadway pavement.
Problems arise quite frequently in the resurfacing of roadways in that a layer of pavement is placed on the existing pavement, resulting in the manhole cover being below the top surface of the new pavement, causing a depression in the roadway. It is quite difficult and expensive to raise the existing manhole frame sufficiently to compensate for the added pavement.
Various devices have been constructed which enable an existing manhole cover to be raised to the level of the new pavement surface without raising the existing manhole frame. Examples of these devices are shown in U.S. Pat. Nos. 1,517,871, 2,346,361, 3,218,943, 3,773,428 and 3,891,337.
Some of these prior art devices, although apparently providing the desired results, are expensive to manufacture due to the number of machining and forming operations required for their fabrication. Likewise, these devices achieve their adjustment and/or clamping engagement with the manhole frame by a threaded screw mechanism which adjustably joins together a plurality of arcuate ring sections, such as shown in U.S. Pat. Nos. 3,218,943 and 3,773,428. Rotation of the threaded screw or screws expands the ring sections outwardly to achieve the desired clamping engagement with the manhole frame wall.
These types of expansion rings present problems if a large amount of expansion is required in that a bending moment or force is exerted at the engagement point of the adjusting screw and its threaded lug which is mounted on the ring due to the natural tendency of the ring to attempt to conform to the circular configuration of the manhole frame wall and the necessary straight line engagement between the adjusting screw threads and the threaded lugs. This bending moment creates considerable binding between the screw and lug of the ring segment and can prevent sufficient rotation of the screw required to securely clamp the support ring in position on the manhole frame. Also, many of these prior elevating ring constructions use an expanding mechanism which protrudes into the internal diameter of the manhole opening, thereby reducing the actual internal diameter, as well as creating a work and safety hazard for workmen climbing into and out of the manhole opening.
Many of these problems existing with present manhole support rings have been eliminated by the manhole cover support ring shown in my above-mentioned U.S. Pat. No. 4,097,171. Although the support ring construction of this patent performs satisfactorily, it can create an undesirable situation in that the toggle links of the expansion mechanism occasionally become damaged during storage and shipment, since the links flap loosely on their pivotal mounting since they are not connected together. Also, the range of hole sizes is somewhat limited in which this toggle-actuated ring construction can be used. Occasionally the toggle links when in an open position, may form too sharp of an angle between the engaged link ends, making it extremely difficult to move the junction point outwardly beyond center to lock the ring in position since this sharp angle requires a large amount of force. Therefore, my improved ring construction which is discussed below and defined in the claims, overcomes the problems existing with prior constructions, including the ring construction of my previous patent.
No manhole cover support ring of which I am aware uses an internal, peripherally mounted, tubular-bolt-actuated mechanism for expanding the support ring outwardly into clamping arrangement within the opening of a manhole frame without placing an undesirable bending moment on the expanding screws or bolts.